A variety of objects, particularly, objects having non-metallic surfaces, can be prone to environmental electromagnetic effects, such as lightning strikes. For example, MIL-STD-464 describes the importance of considering environmental electromagnetic effects (“E3”) when selecting materials for use in military aircraft. More particularly, MIL-STD-464 specifies that all systems, subsystems, and equipment used in constructing an aircraft should be compatible with internal electromagnetic emissions (e.g., electronic noise, RF transmissions, and cross-coupling of electrical currents) and with external electromagnetic emissions (e.g., lightning and electromagnetic pulses).
Typically, metallic aircraft encountering lightning will conduct the electric current of a strike across the skin of the aircraft, in most cases suffering little resultant damage. On the other hand, composite materials like graphite epoxy resins, are resistive conductors that inhibit current conductance. A graphite composite will absorb vastly greater amounts of energy absorbed as compared with by the same mass of aluminum. The intense current density of a lightning strike, can vaporize or “puncture” the thin composite laminates that make up the skin of the aircraft. Once such penetration occurs further damage can be done as the lightning pathway “intrudes” on the avionics, power supply circuitry, or other critical systems, and actual physical damage may result as this current surge travels around and through the inside of the aircraft. Electromagnetic energy may also enter the aircraft through other types of apertures.
Electromagnetic fields that enter the aircraft can wreak havoc with on board avionics. This problem is further aggravated by the increasing use of digital designs in modern avionics to control critical flight functions besides their traditional navigation and communication tasks. It is well known that digital circuits, as compared to analog circuits, have little tolerance for electrical and electromagnetic disturbances. Accordingly, it is important that electromagnetic fields are not permitted to breach the aircraft skin, where they may disrupt avionics, damage structural components, and, perhaps, injure passengers or crew.
Accordingly, a need continues to exist for a method of providing E3 protection for aircraft and other objects. The present invention is directed to meeting this need.